1. Field of the Invention
The present invention relates to an actuator device having a housing and an internal moving body movable within the housing. More specifically, the present invention relates to an actuator device which transmits the movement of the internal moving body to an external moving body disposed on the outside of the housing by a driving member which couples the internal moving body and the external moving body and extends through a slit formed on the wall of the housing.
2. Description of the Related Art
This type of actuator device is known, for example, as a rodless cylinder and an electric linear actuator. In a rodless cylinder, the housing is formed as a cylinder tube and the internal moving body is formed as a piston driven by pressurized fluid, such as air, supplied to the cylinder tube. In an electric linear actuator, on the other hand, the internal moving body is driven by a feed screw extending through the cylinder tube and driven by an electric motor.
The actuator device such as the rodless cylinder and the electric linear actuator are disclosed in various publications.
For example:
(A) Japanese Examined Patent Publication (Kokoku) No. 51-28793 and Japanese Unexamined Utility Model Publication (Kokai) No. 61-200908 disclose rodless cylinders. The rodless cylinders in these publications are provided with a cylinder tube (a cylinder barrel) functioning as a housing. The internal moving body formed as a piston moves within a cylinder chamber (a bore) formed in the cylinder tube along the direction of the axis of the cylinder tube. The movement of the piston is transmitted to an external moving body disposed outside of the cylinder tube by a driving member (a piston yoke) which extends through the slit and couples the external moving body to the internal moving body. The rodless cylinders in the '793 publication and the '908 publication are provided with one cylinder chamber and one slit. PA1 (B) Japanese Unexamined Patent Publication (Kokai) No. 8-261209 discloses a rodless cylinder similar to those in the publications (A). However, the housing (the cylinder tube) is formed as a curved tube. In other words, the central axis of the cylinder tube is not straight but a curved line. PA1 (C) Japanese Unexamined Patent Publication (Kokai) No. 9-210012 and Japanese Patent No. 2675720 disclose rodless cylinders similar to those in the publications (A). However, the rodless cylinders in these publications are provided with a guide rail extending in parallel with the axis of the cylinder tube inorder to guide the external moving body. PA1 (D) U.S. Pat. No. 4,566,738 and Japanese Examined Utility Model Publication (Kokoku) No. 8-4995 disclose electric linear actuators. In these publications, internal moving bodies (runners) are driven by electric motors through feed screws (threaded spindles). Therefore, no pressurized fluid is supplied to the cylinder chamber (the bore). The electric linear actuators in these publications are also provided with one cylinder chamber and one slit through which the driving member extends. PA1 (E) U.S. Pat. No. 2,200,427, Japanese Unexamined Patent Publication (Kokai) No. 60-172711 and U.K. Patent No. 470088 disclose actuating devices having a plurality of cylinder chambers formed in one housing. One internal moving body is disposed in each of cylinder chambers. Further, each of the cylinder chambers is provided with one slit formed in the housing wall and the external moving body is coupled to each of the internal moving bodies by a driving member extending through each slit.
In the actuator devices in the publications (A), (B) and (c), since the internal moving body (the piston) is driven by pressurized fluid, internal pressure is exerted on the wall of the cylinder tube. Further, the slit penetrating the wall of the cylinder tube and communicating with the cylinder chamber (the bore) is provided in this type of the actuator devices. Therefore, the internal pressure exerting on the wall of the cylinder chamber causes a stress concentration in the wall of the housing at the portion opposing the slit. Thus, in this type of the actuating device, it is necessary to increase the thickness of the wall of the housing at the portion opposing the slit. This non-uniform thickness of the wall of the housing makes it difficult to produce the housing by an extrusion process or a drawing process. In addition to that, the shape of the cross section of the housing is such that a large void space which communicates with the outside of the housing through a narrow slit is formed in the housing. This shape of the cross section requires a die having a complicated shape and makes the production of the housing by an extrusion or a drawing process difficult.
Further, the stress concentration and the non-uniformity of the wall thickness requires a complicated calculation of the stress distribution of the wall when designing the housing.
In the actuator device in the publication (B), in order to obtain the housing having a curved center axis, a straight housing must bent in such a manner that the center axis thereof forms a required curve. This bending process is complicated and increases the time and the cost required for manufacturing the housing.
Further, in the actuator devices in the publications (A) to (D), the shape of the cross section of the housing is rather complicated due to the necessity for forming the slit on the wall of the housing. Therefore, even a slight modification of the shape of the cylinder chamber requires a large amount of work in order to achieve desired accuracy in the dimension and the shape of the housing, especially in the modification of the die used for forming the housing. Therefore, time and cost required for developing new products becomes rather large.
Further, since only one slit is provided on the wall of the housing, the internal moving body and the external moving body are coupled by only one driving member in the actuator devices in the publications (A), (B) and (D). Therefore, when a bending moment is exerted on the external moving body, or a external force is exerted on the external moving body in the axial direction (for example, when the external moving body abuts a stopper at its stroke end), the bending moment and the axial force must be born by only one driving member in the actuator device in the publications (A), (B) and (D). Thus, the allowable bending moment and axial force of the actuator device becomes rather small.
In the actuator device in the publication (C), since a separate guide rail is provided, a large bending moment exerted on the external moving body can be born by the guide rail. However, since the guide rail cannot bear the axial force exerted on the external moving body, the allowable axial force of the actuator device in the publication (C) is still small.
In the actuator devices in the publications (E), the external moving body is coupled to the internal moving body by a plurality of driving members. Therefore, in this case, the bending moment and the axial force is distributed to a plurality of driving members and the allowable bending moment and the allowable axial force of the actuator device become larger when compared with the actuator devices in the publications (A) (B) and (D). However, in the actuators in the publications (E), more than one internal moving body must be disposed in the housing. This causes the total cross section area of the internal moving bodies, i.e., the total area receiving the pressure of the working fluid decreases compared with the case where one internal moving body is disposed in the housing of the same size. Therefore, in order to obtain the driving force the same as that of the actuator device having one internal moving body in the housing, a larger housing is required in the actuator device in the publications (E).